Method and composition for rendering material fire resistant



United States Patent 3,463,665 METHOD AND COMPOSITION FOR RENDERING MATERIAL FIRE RESISTANT Patrick D. Quinn, St. Louis, Mo., assignor to American Zinc Company, St. Louis, Mo., a corporation of Maine No Drawing. Filed Apr. 18, 1966, Ser. No. 543,084 Int. Cl. B44d 1/28; C09d 5/18 U.S. Cl. 117-138 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the treatment of fibrous and porous materials. It has particular application to the treatment of wood and fabric, to render those materials resistant to fire. The term fabric is used herein to indicate fibrous sheet materials which may be woven, knitted, felted, laid, or otherwise formed, and to fibers, which may be in the form of yarn, thread, fur, hair, short pieces of stock or the like, which are used to produce these sheet materials. Thus the term fabric includes cloth, (whether of animal fiber, e.g., Wool, silk; vegetable fiber, e.g., cotton, linen; or synthetic fiber, e.g., rayon, nylon) and paper.

While this invention is not limited thereto it has particular application to cellulosic materials.

This invention is related to and constitutes an improvement on the methods and products described in U.S. Patents Nos. 2,838,424 and 2,868,673. As those patents point out, the basic zinc salts, particularly basic zinc chloride and basic zinc sulfate, provide fire resistance in Wood and fabric, and when wood and fabric are impregnated with them in accordance with the methods set out in those patents, in the specified quantities, the wood and fabric are rendered resistant to fire, as well as to decay, insects, and marine borers, even after prolonged leaching in either fresh or salt water.

When wood is impregnated with basic zinc chloride or basic zinc sulfate or a mixture of the two, in accordance with the methods of either of the patents, the unleached wood is adequately resistant to fire if the zinc content is more than 1.5 pounds per cubic foot. If ammonium salts are used, they may supplement the beneficial effect of the zinc salts.

If the treated wood is leached in fresh running water for prolonged periods, the ammonium salts leach out relatively quickly, and the basic chloride and basic sulfate anions are. removed slowly. The zinc, however, remains, and if the zinc content originally was over 2.4 pounds per cubic foot, the wood will meet the test in a fire tube by the method of ASTM E69. The general resistance to flame and heat are good, and weight loss in the fire tube test will be quite acceptable. However, if this leached wood is exposed to an intense flame for such a period that extended areas of glow are generated, these areas will sometimes continue to glow in an air current of 12 miles per hour. These conditions are encountered in every roof deck of impregnated wooden shingles or shakes tested in accordance with the Class C Burning Brand Test of the Underwriters Laboratories, Inc. (ASTM E-l08).

The problem has been clearly defined, but its solution has heretofore escaped the industry. Numerous zinc compounds have been tested heretofore, none of which has produced the required result. For example, zinc borate offers excellent glow resistance, but it is not resistant to leaching. Zinc phosphate and zinc ammonium phosphate possess the needed insolubility at selected pH values, but lack of glow resistance. A combination of these compounds is also ineffective.

One of the objects of this invetnion is to provide a composition and method for treating wood or fabric by which the Wood or fabric is made fire and glow resistant.

Another object is to provide such compositions and method which produce a fire and glow resistant wood which, at the same time, has excellent physical properties and little tendency to cause corrosion of ferrous metals which may be in prolonged contact with the treated wood.

Another object is to provide such composition and method which are adapted to be used in impregnation equipment suitable for handling zinc chloride.

Other objects will become apparent to those skilled in the art in the light of the following description.

In accordance with this invention, generally stated, wood or fabric is impregnated with a zinc salt the anion of which is a complex fluoride, such, for example as zinc silicofiuoride, zinc phosphofiuoride or zinc borofluoride, of which the referred salt is zinc silicofiuoride. In the preferred embodiment, the wood or fabric is impregnated with a mixture of zinc sulfate and zinc silicofiuoride, and the impregnants are insolubilized within the pores or interstices of the impregnated material by one of the methods described in the patents to which reference has been made, U.S. 2,838,424 and 2,868,673. In any case the concentration of zinc in the treating solution should be in the range of 5% to 10% by weight.

The zinc complex fluoride salts are water soluble, as is the zinc sulfate. For example, as much as grams of zinc silicofluoride can be dissolved in grams of warm water, so that the treating solution is easily made up.

The use of zinc sulfate in connection with the zinc complex fluoride salt is particularly felicitous. The treating composition is effective, in the case of wood shakes and shingles, up to a ratio of zinc sulfate to zinc silicofluoride of about 5:1. The preferred range is from 1:1 to 4:1 molar ratio of zinc sulfate to zinc silicofiuoride. The use of the zinc sulfate not only reduces the cost of treatment, but, more importantly minimizes the adverse effect of locally excessive amounts of ammonia (in the form of gaseous ammonia, ammonium hydroxide or the decomposition product of urea) used in insolubilizing the salts. With a 2: 1 molar ratio of zinc sulfate to zinc silicofiuoride, a zinc content of the impregnated shingle of the two pounds per cubic foot of wood before leaching will produce leached shingles which will pass the Class C Burning Brand Test.

Other zinc salts besides zinc sulfates may be added in lieu of the zinc sulfate. While zinc chloride is operative to produce fire and glow resistance, it tends to corrode ferrous metals in contact with treated wood. Therefore, it has been found desirable to avoid chlorides and also to avoid oxidizing anions. The use of cations having more than one valence state should be carefully avoided, also.

The following examples are merely illustrative.

EXAMPLE I An impregnating solution was made up as follows:

Kilograms (A) ZnSiF -6H O 188 H O 318 (B) ZnSO -H O 108.2 H O 398 The zinc silicofluoride is dissolved in the water to form the solution (A). The zinc sulfate is dissolved in the water to form the solution (B). Each of the solutions contains 39 kilograms of zinc. The two solutions are then mixed to form a solution with a 1:1 molar ratio of zinc silicofluoride and zinc sulfate, and a 7.7% concentration, by weight, of zinc in the solution.

Bundles of red cedar shingles were placed in a treating cylinder. The treating cylinder was filled with the impregnating solution through a pressure-measuring tank connected to the treating cylinder. Air pressure was then applied, through the pressure-measuring tank to the solution in the treating cylinder, at approximately 100 pounds per square inch gauge, to force the solution into the pores of the shingles. The amount of solution introduced to the treating cylinder is accurately measured through the measuring tank.

Approximately an hour after the pressure stabilized indicating that the shingles were impregnated, the solution remaining was blown back to a storage tank. A vacuum of 25" of mercury was applied for one half hour to wipe excess solution from the shingles. The shingles were permitted to stand overnight in the treating cylinder, at atmospheric pressure, to permit excess solution to drain out. The total amount of unabsorbed solution was measured, the difference between the amount introduced and the amount removed from the cylinder being a measure of the amount absorbed by the shingles.

In this particular experiment, the shingles were then removed from the treating cylinder, weighed, and permitted to dry, partially, in the air, for one hour. They were then replaced in the cylinder. A vacuum of 25" of mercury was then applied for one half hour, after which gaseous ammonia in the amount of '2 moles of ammonia to 1 mole of zinc, was introduced. In terms of weight, .78 kilograms of ammonia was introduced for each kilogram of zinc absorbed in the shingles.

The shingles were permitted to remain in the test cylinder, with the ammonia, overnight, which ensured complete reaction of the ammonia with the zinc salts, so that little offensive ammoniacal odor was given off by the shingles.

The shingles were then removed and permitted to air dry. They contained 2.02 pounds of zinc per cubic foot of wood.

The shingles, in bundles arranged with every shingle spaced to permit the circulation of water, were then leached in running tap water for two weeks, dried, nailed on test roofs, and subjected to the Class C Burning Brand Test to which reference has been made. This test is the same as the fire test of roof covering ASTM E-l08. The leached shingles of this example pass the test.

For red cedar shingles in general, about eight to nine percent zinc in the treating solution is preferred. Six and a half percent has been found satisfactory for the treatment of high pick-up shingles. A higher percentage of zinc than nine is quite operative but needlessly expensive.

The partial drying step between the impregnation with the solution and the insolubilization of the impregnant with the ammonia, in the tWo step process described in Example 1, has advantages in saving of material. When anhydrous ammonia is absorbed in water, the absorption is accompanied by a large expansion in volume. If free impregnating solution is present in the pores, this expansion tends to cause bleeding. By evaporating much of the water, all but a trace of the bleeding can be eliminated.

For further examples, one may merely substitute the use of the impregnate solution of Example 1, varied, if desired, between a 1 molar ratio of zinc sulfate to zinc silicofluoride and -1 ratio, or the zinc borofluoride or phosphofluoride substituted, in the various examples given in Depew et al. U. S. 2,838,424 and 2,868,673.

Thus, a solution made up of 94 kilos of zinc silicofluoride, 159 kilos of water, 108.2 kilos of zinc sulfate and 398 kilos of water (a 2-1 molar ratio of zinc sulfate zinc silicofluoride) can be used instead of the zinc chloride solution in Example 2 of Patent No. 2,868,673. The solution of Example 1 can be substituted for the 40% zinc chloride solution of the Example IX of Patent 2,868,673 to produce a cloth which has excellent fire and glow resistant characteristics. Such a treated cloth can be used in applications where the hand of the cloth is of relatively little importance. In using the solution of this invention, as exemplified in Example 1, in the process described in Patent No. 2,838,424 an amount of 9.5% urea may simply be added to and dissolved in the solution to produce treated wood with the superior characteristics of this invention.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. A method of treating wood comprising impregnating the wood with an aqueous solution of a zinc complex fluoride salt, the concentration of zinc in said solution being between 5% and 10% by weight, and thereafter reacting said salt with a base, thereby insolubilizing said zinc complex fluoride salt in situ.

2. The method of claim 1 wherein the zinc complex fluoride salt is taken from the group consisting of zinc silicofluoride, zinc borofiuoride and zinc phosphofiuoride.

3. The method of claim 1 wherein the zinc complex fluoride is zinc silicofluoride.

4. The method of claim 3 wherein the aqueous solution comprises a mixture of the zinc silicofluoride, and another water soluble zinc salt taken from the group consisting of zinc sulfate and zinc chloride, the mole ratio of the other zinc salt to the zinc silicofluoride being no greater than 5:1.

5. A treating solution for rendering material fire and glow resistant consisting essentially of zinc silicofluoride and zinc sulfate dissolved in water, said zinc salts being present in the range of molar proportion of 1:1 zinc sulfate to zinc silicofluoride to 5:1 zinc sulfate to zinc silicofluoride, the concentration of zinc in said solution being between 5% and 10% by weight.

6. A method of treating wood comprising impregnating the wood with an aqueous solution of zinc silicofluoride, the concentration of zinc in said solution being between 5% and 10% by weight, and thereafter reacting said zinc silicofluoride with the ammoniacal base, thereby insolubilizing the zinc silicofluoride in situ.

7. A treating solution for rendering material fire and glow resistant consisting essentially of zinc silicofluoride and another water soluble zinc salt taken from the group consisting of zinc sulfate and zinc chloride, dissolved in water, said zinc salts being present in the range of molar proportions of 1:1 other zinc salt to zinc silicofluoride to 5:1 other zinc salt to zinc silicofluoride, the concentration of zinc in said solution being between 5% and 10% by weight.

References Cited UNITED STATES PATENTS 2,128,782 8/1938 Miiller 117-138 XR 2,152,160 3/1939 Steinherz 117151 XR 2,838,424 6/1958 Depew et al. 117-138 XR 2,868,673 1/1959 Depew et al. 117138 XR 3,242,000 3/1966 Lynch 117-138 XR WILLIAM D. MARTIN, Primary Examiner H. I. GWINNELL, Assistant Examiner 

